1. Field of Invention
The present invention relates to the field of nonaqueous electrolytic solutions and batteries using the same. More particularly, this invention pertains to nonaqueous electrolytic solutions comprising (a) one or more solvents; (b) one or more ionic salts; and (c) one or more amine oxides. Rechargeable batteries comprising such nonaqueous electrolytic solutions are disclosed herein as well as methods of making nonaqueous electrolytic solutions with amine oxides to scavenge moisture and free acid in lithium batteries and lithium ion batteries.
2. Description of Related Art
Electric current producing cells such as batteries consist of pairs of electrodes of opposite polarity separated by electrolytic solution, which includes a solvent and a solute. The charge flow between electrodes is maintained by an ionically conducting solute, i.e., a salt. The non-aqueous electrolytic solutions, which are used in lithium and lithium ion batteries, are made by dissolving lithium salts in a variety of organic solvents. In particular, nonaqueous electrolytes comprising lithium hexafluorophosphate (LiPF6) exhibit very good electrochemical stability and conductivity. However, LiPF6 is not thermally stable and readily decomposes by hydrolysis, as set forth in the following well-known reactions:LiPF6→LiF+PF5  (1)LiPF6+H2O→2HF+LiF+POF3  (2)
Thermal decomposition of LiPF6 occurs at elevated temperatures (Reaction 1), and is accelerated in solution due to the reactions of PF5 and solvents. Hydrolysis (Reaction 2) generally occurs due to moisture and acidic impurities in the lithium salt and electrolytic solution. Accordingly, both water and hydrogen fluoride (HF) are undesirable in lithium and lithium-ion battery systems. The strong acid HF is especially harmful to batteries because it reacts with electrode active materials and corrodes the solid electrolyte interface (SEI), which results in poor battery performance. Thus the performance of such an electrolytic solution, and hence of a battery made therewith, is not optimal.
On the other hand, due to the large difference between the polarity of cyclic esters such as ethylene carbonate (EC), propylene carbonate (PC), and gamma-butyrolactone (GBL) and the polarity of polypropylene and/or polyethylene separator membranes, the electrolyte solution cannot achieve very good wetting of the polypropylene and/or polyethylene separator membrane. Thus the performance of the electrolytic solution, and hence of the battery made therewith, is not optimal.